A rubber seal material is extensively used as a general seal material that can easily ensure a sealing property by a low tightening force. For instance, a rubber seal material is used as a seal material for a semiconductor manufacturing apparatus or a gate valve for vacuum in a liquid crystal manufacturing apparatus.
A rubber seal material is in a shape of an O ring or lip packing in a general way. In addition, seals having an irregular cross section that are disclosed in Patent documents 1 to 3 for instance are used in many cases.    Patent document 1: Japanese Patent Application Laid-Open Publication No. 10-318373    Patent document 2: Japanese Patent Publication No. 3050919    Patent document 3: Japanese Patent Application Laid-Open Publication No. 2004-316724
A high temperature processing is carried out for a semiconductor manufacturing apparatus in some cases. At that time, an anchoring fixation may occur between a seal and a matching sealing surface disadvantageously. The anchoring fixation means a phenomenon in which a rubber seal and a matching sealing surface of a metal or the like come into contact with each other for a long period of time under the conditions of a high temperature and a high pressure and the rubber seal material and the matching sealing surface are jointed together physically and chemically, whereby a force that is required for separating the seal (a fixing force) is increased. In the case in which a metal seal is used in order to avoid the problem of the anchoring fixation, a great deal of load is required for tightening the seal material and it is necessary to increase the size of the apparatus. Consequently, it is desired to suppress an influence of fastening while a seal made of a rubber or the like is used.
The present invention was made in consideration of such conditions, and an object of the present invention is to provide a seal that can be easily separated from a matching sealing surface even in the case in which the seal material is used for a long period of time under the conditions of a high temperature and a high pressure for instance.